In-vitro and in-vivo characterization of a buprenorphine delivery system

Buprenorphine is a mu-opioid receptor partial agonist with enhanced safety and comparable efficacy to methadone for treatment of opioid dependence. The sublingual formulation of buprenorphine, approved for treatment of opioid dependence, produces variable buprenorphine blood levels and requires frequent dosing that limits patient compliance. To achieve stable buprenorphine levels that may improve patient outcome, an implantable sustained buprenorphine delivery system was developed. Each implant consists of ethylene vinyl acetate copolymer and 90 mg buprenorphine HCl, and measures 26 mm in length and 2.4 mm in diameter. Steady-state release in-vitro was 0.5 mg/implant/day. In-vivo pharmacokinetics and safety were examined for up to 52 weeks in beagle dogs receiving 8, 16 or 24 subcutaneous implants. Plasma buprenorphine concentrations correlated with the number of implants administered. Peak buprenorphine concentrations were generally reached within 24 h after implantation. Steady-state plasma levels were attained between 3 and 8 weeks, and were maintained for study duration, with a calculated mean release rate of 0.14+/-0.04 mg/implant/day. There were no test-article-related adverse effects. This delivery system can provide long-term stable systemic buprenorphine levels, and may increase patient compliance, thereby improving outcome for opioid-dependent patients.